feat: Implement air-gap functionality with timeline impact and evidence snapshot services

- Added AirgapTimelineImpact, AirgapTimelineImpactInput, and AirgapTimelineImpactResult records for managing air-gap bundle import impacts.
- Introduced EvidenceSnapshotRecord, EvidenceSnapshotLinkInput, and EvidenceSnapshotLinkResult records for linking findings to evidence snapshots.
- Created IEvidenceSnapshotRepository interface for managing evidence snapshot records.
- Developed StalenessValidationService to validate staleness and enforce freshness thresholds.
- Implemented AirgapTimelineService for emitting timeline events related to bundle imports.
- Added EvidenceSnapshotService for linking findings to evidence snapshots and verifying their validity.
- Introduced AirGapOptions for configuring air-gap staleness enforcement and thresholds.
- Added minimal jsPDF stub for offline/testing builds in the web application.
- Created TypeScript definitions for jsPDF to enhance type safety in the web application.

src/Findings/StellaOps.Findings.Ledger/Observability/LedgerTimeline.cs

@@ -15,6 +15,8 @@ internal static class LedgerTimeline
     private static readonly EventId ProjectionUpdated = new(6201, "ledger.projection.updated");
     private static readonly EventId OrchestratorExport = new(6301, "ledger.export.recorded");
     private static readonly EventId AirgapImport = new(6401, "ledger.airgap.imported");
+    private static readonly EventId EvidenceSnapshotLinkedEvent = new(6501, "ledger.evidence.snapshot_linked");
+    private static readonly EventId AirgapTimelineImpactEvent = new(6601, "ledger.airgap.timeline_impact");
 
     public static void EmitLedgerAppended(ILogger logger, LedgerEventRecord record, string? evidenceBundleRef = null)
     {
@@ -99,4 +101,47 @@ internal static class LedgerTimeline
             merkleRoot,
             ledgerEventId?.ToString() ?? string.Empty);
     }
+
+    public static void EmitEvidenceSnapshotLinked(ILogger logger, string tenantId, string findingId, string bundleUri, string dsseDigest)
+    {
+        if (logger is null)
+        {
+            return;
+        }
+
+        logger.LogInformation(
+            EvidenceSnapshotLinkedEvent,
+            "timeline ledger.evidence.snapshot_linked tenant={Tenant} finding={FindingId} bundle_uri={BundleUri} dsse_digest={DsseDigest}",
+            tenantId,
+            findingId,
+            bundleUri,
+            dsseDigest);
+    }
+
+    public static void EmitAirgapTimelineImpact(
+        ILogger logger,
+        string tenantId,
+        string bundleId,
+        int newFindings,
+        int resolvedFindings,
+        int criticalDelta,
+        DateTimeOffset timeAnchor,
+        bool sealedMode)
+    {
+        if (logger is null)
+        {
+            return;
+        }
+
+        logger.LogInformation(
+            AirgapTimelineImpactEvent,
+            "timeline ledger.airgap.timeline_impact tenant={Tenant} bundle={BundleId} new_findings={NewFindings} resolved_findings={ResolvedFindings} critical_delta={CriticalDelta} time_anchor={TimeAnchor} sealed_mode={SealedMode}",
+            tenantId,
+            bundleId,
+            newFindings,
+            resolvedFindings,
+            criticalDelta,
+            timeAnchor.ToString("O"),
+            sealedMode);
+    }
 }